Anthelmintic resistance in equine parasites--current evidence and knowledge gaps

Area of Science:

• Veterinary Parasitology
• Equine Health
• Drug Resistance

Background:

• Anthelmintic resistance in equine nematodes has been documented since the 1960s.
• Limited specific evidence exists for equine parasites, with knowledge often extrapolated from sheep parasites.
• The complexity of multiple cyathostomin species in horses complicates resistance studies.

Purpose of the Study:

• To review the factors influencing anthelmintic resistance development in equine nematodes.
• To highlight the complexities and knowledge gaps in understanding equine parasite drug resistance.
• To emphasize the need for further research and standardized diagnostic guidelines.

Main Methods:

• Literature review of existing studies on anthelmintic resistance in equine nematodes.
• Analysis of factors contributing to resistance, including parasite biology and host-parasite interactions.
• Evaluation of current diagnostic approaches and their limitations.

Main Results:

• Factors influencing resistance include parasite seasonality, lifespan, fecundity, host immunity, and encysted stages.
• Parasite refugia likely play a significant role in resistance development.
• Drug-resistant strains appear to have no significant fitness cost.
• Current in vitro and molecular diagnostic assays have shown limited success.

Conclusions:

• Understanding anthelmintic resistance in equine nematodes is complex.
• Standardized guidelines for fecal egg count reduction tests are needed.
• Further research is essential to address the growing challenge of drug resistance in horses.